Typically, in a semiconductor device, various electronic components (e.g., transistors, diodes, resistors, capacitors, and the like) are formed in device dies on a wafer. These device dies may then be sawed and bonded to other device dies to form functional devices. For example, in image sensing technologies, a complementary metal-oxide semiconductor (CMOS) image sensor (CIS) may include pixel arrays (e.g., connected to photo diodes) formed on one device die, and logical control circuits may be formed on another device die. These separate dies may be bonded together using a hybrid bonding process to form a functional device. Hybrid bonding is also used in other applications to form three dimensional integrated circuits (3DICs) where multiple dies are stacked on one another.
In hybrid bonding, conductive pads on a top surface of one die may be directly bonded to conductive pads on a top surface of the other die, for example, using fusion bonding and annealing processes. However, as a result of the annealing process, the material of the conductive pads may be stretched (e.g., as a result of increased ductility) and voids may be formed between the bonded conductive pads, especially in the corner regions.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.